Spring Boot has become a cornerstone of modern Java development, offering a rapid application development (RAD) platform that simplifies the creation of standalone, production-grade Spring-based applications. If you’re looking for a Spring Boot developer role, check out the top 20 Spring Boot interview questions and answers for experienced developers and freshers.
Spring Boot interview questions and answers
1. What is Spring Boot, and how is it different from the Spring Framework?
2. What is the Spring Boot Starter?
3. What is auto-configuration in Spring Boot?
4. How do you disable a specific auto-configuration in Spring Boot?
5. What are the main annotations used in Spring Boot?
6. What is an embedded server in Spring Boot?
7. What are Spring Boot Actuator and its use cases?
8. How do you externalize configuration in Spring Boot?
9. What is the use of @SpringBootApplication?
10. How do you create a RESTful service using Spring Boot?
11. How do you handle exceptions in Spring Boot?
12. What is a Spring Boot Starter Parent?
13. What is DevTools in Spring Boot?
14. How does Spring Boot manage dependencies?
15. How can you secure a Spring Boot application?
16. What is the difference between @RestController and @Controller?
17. What is @ConfigurationProperties in Spring Boot?
18. What is Spring Boot CLI?
19. How can you monitor a Spring Boot application in production?
20. How do you create a custom Starter in Spring Boot?
1. What is Spring Boot, and how is it different from the Spring Framework?
Answer:
Spring Boot is a framework built on top of the Spring Framework that simplifies the development of standalone, production-ready Spring applications. Unlike Spring Framework, Spring Boot provides embedded servers (like Tomcat), starter dependencies, and auto-configuration to minimize configuration effort.
Key differences:
- Auto-Configuration: Spring Boot automatically configures the application based on dependencies.
- Embedded Server: Spring Boot applications can run on embedded servers like Tomcat or Jetty without external server setup.
- No XML Configuration: Spring Boot eliminates the need for XML configuration.
2. What is the Spring Boot Starter?
Answer:
Starters are dependency descriptors that simplify adding specific technology to Spring Boot applications. For example, spring-boot-starter-web includes dependencies for building web applications using Spring MVC, embedded Tomcat, etc.
3. What is auto-configuration in Spring Boot?
Answer:
Auto-configuration is a feature in Spring Boot that automatically configures beans based on classpath settings, other beans, and various property settings. For example, if spring-boot-starter-web is in the classpath, Spring Boot auto-configures components required for a web application (like DispatcherServlet).
4. How do you disable a specific auto-configuration in Spring Boot?
Answer:
To disable a specific auto-configuration, you can use the @EnableAutoConfiguration annotation with the exclude attribute.
@SpringBootApplication
@EnableAutoConfiguration(exclude = { DataSourceAutoConfiguration.class })
public class MyApp { }
5. What are the main annotations used in Spring Boot?
Answer:
@SpringBootApplication: A combination of@Configuration,@EnableAutoConfiguration, and@ComponentScan.@RestController: A convenience annotation for RESTful web services that combines@Controllerand@ResponseBody.@RequestMapping: Maps HTTP requests to handler methods.@EnableAutoConfiguration: Enables auto-configuration in Spring Boot.@Entity: Marks a class as a JPA entity.
6. What is an embedded server in Spring Boot?
Answer:
Spring Boot applications come with embedded servers like Tomcat, Jetty, or Undertow, meaning the server is bundled within the application. This allows you to run the application directly without requiring external server setup.
7. What are Spring Boot Actuator and its use cases?
Answer:
- Spring Boot Actuator provides monitoring and management endpoints for production-ready applications. It offers metrics, health checks, application info, and the ability to track various system and custom metrics.
- Common endpoints include
/actuator/health,/actuator/metrics, and/actuator/env.
8. How do you externalize configuration in Spring Boot?
Answer:
Spring Boot allows externalized configuration through properties files (application.properties or application.yml), environment variables, and command-line arguments. The configuration values can be injected using @Value or @ConfigurationProperties.
9. What is the use of @SpringBootApplication?
Answer:
@SpringBootApplication is a combination of three annotations:
@Configuration: Marks the class as a source of bean definitions.@EnableAutoConfiguration: Enables auto-configuration.@ComponentScan: Enables component scanning to detect@Component,@Service,@Repository, and@Controllerannotations.
10. How do you create a RESTful service using Spring Boot?
Answer:
Annotate the class with @RestController and define request mappings using @RequestMapping or specialized annotations like @GetMapping, @PostMapping, etc.
@RestController
public class MyController {
@GetMapping("/hello")
public String hello() {
return "Hello, World!";
}
}
11. How do you handle exceptions in Spring Boot?
Answer:
You can handle exceptions using @ControllerAdvice and @ExceptionHandler to centralize exception handling.
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleException(Exception ex) {
return new ResponseEntity<>(ex.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);
}
}
12. What is a Spring Boot Starter Parent?
Answer:
The spring-boot-starter-parent is a parent project provided by Spring Boot. It includes default configurations for dependency management, plugin configurations, and a BOM (Bill of Materials) to manage version compatibility for Spring dependencies.
13. What is DevTools in Spring Boot?
Answer:
Spring Boot DevTools is a development tool that improves the development experience by enabling hot reloading, automatic restarts, and live reload of static resources, among other features.
14. How does Spring Boot manage dependencies?
Answer:
Spring Boot simplifies dependency management using starters and a curated list of dependencies via its Bill of Materials (BOM). These ensure compatibility between different versions of libraries used in a Spring Boot project.
15. How can you secure a Spring Boot application?
Answer:
You can secure a Spring Boot application using Spring Security. By including spring-boot-starter-security, basic authentication and form-based authentication are enabled by default. You can customize it via a security configuration class.
@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http.authorizeRequests()
.antMatchers("/public").permitAll()
.anyRequest().authenticated()
.and().formLogin();
}
}
16. What is the difference between @RestController and @Controller?
Answer:
@RestControlleris a specialized version of@Controller. It automatically serializes the returned object into JSON or XML and adds the@ResponseBodyannotation to the method, which means the response is written directly to the HTTP response body.@Controlleris used in Spring MVC for handling web requests and typically returns a view name.
17. What is @ConfigurationProperties in Spring Boot?
Answer:
@ConfigurationProperties is used to map properties from configuration files (application.properties or application.yml) to a Java object. It helps in managing application configuration in a structured way.
@ConfigurationProperties(prefix = "app")
public class AppConfig {
private String name;
// getters and setters
}
18. What is Spring Boot CLI?
Answer:
Spring Boot CLI is a command-line tool that helps in quickly building Spring applications using Groovy. It allows you to run Groovy scripts, which makes the development process faster by reducing the amount of code needed.
19. How can you monitor a Spring Boot application in production?
Answer:
You can monitor a Spring Boot application using Spring Boot Actuator, which exposes various monitoring and management endpoints like /actuator/metrics, /actuator/health, /actuator/loggers, etc. Additionally, you can integrate external monitoring systems like Prometheus or Grafana.
20. How do you create a custom Starter in Spring Boot?
Answer:
- To create a custom starter, you need to create a Maven or Gradle project and define dependencies in
pom.xmlorbuild.gradle. Then you can create the auto-configuration class using@Configurationand expose the beans you want. - You will also need to add
spring.factoriesunderMETA-INFto register your auto-configuration.
These questions cover a wide range of topics, from basic concepts to advanced configurations, and should help you feel well-prepared for a Spring Boot interview.
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